Category: Memory

Finding a specific memory in your brain is not easy. Is it held within a particular group of neurons? If so, which ones? Are they clustered together, or spread throughout the brain? In science-fiction, a goofy helmet and a fancy operating system is all it takes. In real life, we need a subtler and cleverer technique.

Two independent groups of scientists have devised just such a method, and used it to awaken specific memories in mice. One group even planted a slightly artificial memory. These techniques have great promise. They will allow us to study how memories are formed, how our existing memories affect the creation of new ones, and what happens during the simple act of remembering.

Scientists have long been able to reactivate old memories, but only in a crude and undirected way. Back in the 1940s, brain surgeon Wilder Penfield found that when he electrified the brains of some epileptic patients, they recalled vivid random memories. The results were scattershot, and expectedly so. Even the tiniest of electrodes will shock thousands of neurons. There’s no way of directing the electricity to the specific neurons involved in any particular memory.

London is not a good place for fans of right angles. People who like the methodical grid system of Manhattan will whimper and cry at the baffling knot of streets of England’s capital. In this bewildering network, it’s entirely possible to take two right turns and end up in the same place. Or in Narnia. Even with a map, some people manage to get lost. And yet, there are thousands of Londoners who have committed the city’s entire layout to memory – cab drivers.

Piloting London’s distinctive black cabs (taxis to everyone else) is no easy feat. To earn the privilege, drivers have to pass an intense intellectual ordeal, known charmingly as The Knowledge. Ever since 1865, they’ve had to memorise the location of every street within six miles of Charing Cross – all 25,000 of the capital’s arteries, veins and capillaries. They also need to know the locations of 20,000 landmarks – museums, police stations, theatres, clubs, and more – and 320 routes that connect everything up.

It can take two to four years to learn everything. To prove their skills, prospective drivers make “appearances” at the licencing office, where they have to recite the best route between any two points. The only map they can use is the one in their head. They even have to narrate the details of their journey, complete with passed landmarks, road names, junctions, turns and maybe even traffic lights. Only after successfully doing this, several times over, can they earn a cab driver’s licence.

Given how hard it is, it shouldn’t be surprising that The Knowledge changes the brains of those who acquire it. And for the last 11 years, Eleanor Maguire from University College London has been studying those changes.

As we get older, our memories start to fail us. The symptoms of this decline are clear, from losing track of house keys to getting easily muddled and confused. Many of these problems stem from a failure of working memory – the ability to hold pieces of information in mind, block out distractions and stay focused on our goals. Now, a team of American scientists has discovered one of the reasons behind this decline, and a way of potentially reversing it.

Our working memory depends on an area known as the prefrontal cortex or PFC, right at the front of the brain. The PFC contains a network of nerve cells called pyramidal neurons that are all connected to one another and constantly keep each other buzzing and excited – like a neural version of Twitter. This mutual stimulation is the key to our working memory. As we age, the buzz of the pyramidal neurons gets weaker, and information falls more readily from our mental grasp.

But this decline isn’t the fault of the neurons themselves. By studying monkeys, Min Wang from the Yale University School of Medicine has found that the environment around the neurons also changes with age. And by restoring that environment to a more youthful state, he managed to ease some of the age-related decline in working memory.

Information has never been easier to find or record. Within seconds, the Internet lets us find answers to questions that would have remained elusive just a few decades ago. We don’t even have to remember the answers – we can just look them up again.

Now, three psychologists have shown how our memories might react to this omnipresent store of information. They have found that when American students expect to have access to information in the future, they remember that information less well. But there’s a positive flipside: they’re also better at remembering where to find the information again.

[This is the first of three intertwined posts on PKMzeta – the molecule that keeps our memories intact]

We’re used to the idea that we become more forgetful with age. As time passes, our memories naturally fade and weaken, and that’s if we’re lucky enough to avoid traumatic accidents or diseases like Alzheimer’s. But Reut Shema, from the Weizmann Institute of Science in Israel, has found a possible way of preventing this decline, and even reversing it.

By loading the brains of rats with a protein called PKMzeta, she managed to strengthen their memories, even old and faded ones. “Multiple old memories were robustly enhanced. These results have no precedent,” says Todd Sacktor, who led the study together with Yadin Dudai.

PKMzeta is the engine of memory. This single protein behaves like a machine that constantly works to keep our memories intact. Switch it off, and we forget things permanently. It’s our lone defence against a constant tide of forgetfulness that threatens to revert our brains back to a blank slate (see “Exposing the memory engine”).

[This is the second of three intertwined posts on PKMzeta – the molecule that keeps our memories intact]

You’ve got the phone number of a hot date – a vital piece of information that you need to keep in a safe place. You write it in a notepad, you save it on a file in your computer and you try to commit it to memory. This third method – the one involving your brain – is very different to the others.

In the other formats, stability is the norm. The ink on the paper won’t vanish (at least not for centuries). The magnetic information on the hard drive won’t spontaneously rearrange itself. Unless either material suffers physical damage, the information recorded within them will stand the test of time. In your brain, the fate of information is much less certain.

In the last decade, scientists have found that it takes active and unrelenting effort to keep our memories intact. Even long-term memories are constantly on the verge of being erased. To keep them stable, we need to continually recreate a protein called PKMzeta. This molecule is the engine of memory, constantly whirring to store information in our brains. Give the engine a boost, and old memories gain a new lease on life. Switch it off, and we forget things…. permanently.

[This is the third of three intertwined posts on PKMzeta – the molecule that keeps our memories intact]

Last year, I interviewed Todd Sacktor for a feature on fear and memory in Eureka, the Times’s monthly science supplement. Sacktor discovered that a protein called PKMzeta is vital for storing memory and in his latest study, he shows that adding more of this protein in the brain can strengthen even old, faded memories. (See “Single protein can strengthen old faded memories”).

This post collates my two interviews with Sacktor – the first was done last year, and the second last night. The transcripts should act as a companion piece to my news story on his latest study, and my longer feature explaining the history of PKMzeta research and details about how this “memory engine” works.

The business of encoding new memories is more like writing a document on a computer than inscribing words onto paper. Until you save the file, there’s a chance that you could lose the information. This vulnerable window can last for a couple of days. Only after that point does the memory become strong and long-lasting. This is called ‘consolidation’.

It’s not a permanent state. Whenever we remember something, the fragile window reopens. Again, it’s more like opening a computer document than getting notes out of a drawer. You could easily add, edit or delete information at a flick of a key. Every time we bring back an old memory, we run the risk of changing it. Again, it takes a while for this window of opportunity to close, for the reactivated memory to strengthen once more. This is called ‘reconsolidation’.

In the last week, two groups of scientists have found two very different ways of boosting both processes, to produce stronger memories.

There’s a chemical that can subtly shift your childhood memories of your own mother. In some people, it paints mum in a more saintly light, making them remember her as closer and more caring. In others, the chemical has a darker influence, casting mum as a less caring and more distant parent.

All of this becomes heavily ironic when you consider that the chemical in question – a hormone called oxytocin – is often billed as the “hormone of love”, and even marketed as “Liquid Trust”. As a new study shows, the reality is much more complicated. Describing oxytocin as the “hormone of love” is like describing a computer as a “writing tool” – it does other things too, some of which aren’t pleasant.